ArcGIS Engine Developer Guide

VISUAL C++
The following issues with events are documented
on the MSDN Knowledge Base when using
IDispEventImpl. Fixes to ATL code are shown in
MSDN for these issues; however, it is not always
desirable to modify or copy ATL header files. In
this case, IDispEventSimpleImpl can be used
instead.
BUG: Events Fail in ATL Containers when Enum
Used as Event Parameter (Q237771)
BUG: IDispEventImpl Event Handlers May Give
Strange Values for Parameters (Q241810)
BEGIN_SINK_MAP(CMyDialog)
// Make sure the Event Handlers have __stdcall calling convention.
// The 0x1 is the Dispatch ID of the OnMouseDown method.
SINK_ENTRY(IDC_MAPCONTROL1, 0x1, OnMouseDownMapcontrol1)
END_SINK_MAP()
};
Using IDispEventSimpleImpl to listen to events
As the name of this template suggests, it is a simpler version of IDispEventImpl.
The type library is no longer used to turn the IDispatch arguments into a C++
method call. While this may be a simpler implementation, it now requires the
developer to supply a pointer to a structure describing the format of the event
parameters. This structure is typically placed in the .cpp file. For example, here is
the structure describing the parameters of an OnMouseDown event for the
MapControl:
_ATL_FUNC_INFO g_ParamInfo_MapControl_OnMouseDown =
{
CC_STDCALL,
// Calling convention
VT_EMPTY,
// Return type
6, // Number of arguments
{VT_I4, VT_I4, VT_I4, VT_I4, VT_R8, VT_R8} // VariantArgument types
};
The header file now inherits from IDispEventSimpleImpl and uses a different
macro, SINK_ENTRY_INFO, in the SINK_MAP. Also, the events interface ID is
required; #import can be used to define this symbol. Note that a dispatch interface
is normally prefixed with DIID instead of IID.
#pragma once
See the ‘Importing ArcGIS type libraries’ section
earlier in this chapter for an explanation of
#import.
#include "resource.h" // Main symbols
#include
// Reference to structure defining event parameters
extern _ATL_FUNC_INFO g_ParamInfo_MapControl_OnMouseDown;
////////////////////////////////////////////////////////////////////////////
// CMyDialog2
class CMyDialog2 :
public CAxDialogImpl,
public IDispEventSimpleImpl
{
public:
// Message handler code removed, it is the same as CMyDialog using
IDispEventSimple
BEGIN_SINK_MAP(CMyDialog2)
// Make sure the Event Handlers have __stdcall calling convention.
// The 0x1 is the Dispatch ID of the OnMouseDown method.
SINK_ENTRY_INFO(IDC_MAPCONTROL1, // ID of event source
132 • ArcGIS Engine Developer Guide